To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
In a mobile communication system, random-access operation of a terminal may be performed when uplink synchronization is performed. Content-based random access is a method in which a terminal randomly selects and transmits a preamble, and collisions may occur when two or more terminals simultaneously transmit the same preamble. According to a contention-based random-access procedure, a terminal attempts random access (transmits a preamble through an access channel) when the terminal needs to obtain uplink synchronization, and a base station may transmit, to the corresponding terminal, a response (random-access response) message in response to the random access. Then, the terminal transmits a random-access procedure message (L2/L3 message), such as an RRC access request message, a tracking area update message, a scheduling request message, and the like, to the base station, and the base station may generate a contention release message to distinguish a terminal corresponding to a recognized preamble, and transmit the same to the corresponding terminal based on a HARQ scheme.
When the terminal attempts the contention-based random access, the terminal performs random access by selecting a preamble that may be used by a plurality of terminals. In this instance, when a plurality of terminals attempts random access, collisions occur, and thus the random access fails. When the terminal attempts random access and does not receive a random-access response (RAR) message within a predetermined period of time (random-access response window), the terminal determines that the random access has failed. The terminal may reattempt random access by increasing transmission power of a preamble. The terminal may transmit a preamble by increasing transmission power until receiving an RAR message from the base station. When the terminal transmits a preamble at the maximum transmission power, the terminal may transmit a preamble by decreasing transmission power to initial transmission power.